There's a difference between "top tier" units and USEFUL units. A-rank units are not useful for anything. You simply can't put them in your team at all. In all those games you mentioned, you can at least find a use for the pull. I'm not saying I need Gram with each pull, but I need better than a stupid A rank unit that is fused away (and the fuse failed).
Well in the case of P&D this simply isnt true, if (when) you pull 3 or 4* junk there is next to no use for it, the best you can do is attempt to use it for a skill-up, which has a much lower chance of success than using an A to enhance a unit. Most of the big mobile games are the same, and most arent as good about giving free premium currency as this one (though I have to say, Im finding that rubies are drying up now that Ive got all the rapport ones I can and unless you place really high in weeklies)